The Dorsal Column-Medial Lemniscal System Learning Module Click to Begin

Used with permission of the Academy of Neurologic Physical Therapy of the APTA Do not duplicate without acknowledging Learning Activity author Michael McKeough, PT, EdD

Contents Overview Introduction Learning Objectives Instructions Legend Read these Instructions! Dorsal Column-Medical Lemniscal System Fasciculus gracilis Fasciculus cuneatus Lesion lessons Fasciculus gracilis lesion Fasciculus cuneatus lesion Dorsal column lesion Medial lemniscus lesion Internal capsule lesion Patient Cases Case 1 Case 2 Case 3 Contents DCML Lesions Patient Cases Exit

Overview Introduction Learning Objectives Instructions Legend Contents DCML Lesions Patient Cases Exit

Introduction This module reviews the Dorsal Column-Medial Lemniscal System (DCML). Module organization consists of three components. Overview consists of this Introduction and the Learning Objectives. Contents consists of Navigation Instructions, a Legend, Review of the normal structure and function of the DCML, and 5 interactive lesion lessons. Cases consists of Instructions and 3 interactive patient cases with feedback. At the bottom of each page a navigation bar contains options to move throughout the module. Material is presented at both the behavioral level and the neuroanatomical level. The behavioral level is presented first and depicts a patient’s clinical presentation. The neuroanatomical level depicts the detailed anatomy of first-order, second-order and third-order neurons. The neuroanatomical level accounts for the patient’s behavioral presentation on examination under normal and lesioned conditions. Contents DCML Lesions Patient Cases Exit

Learning Objectives After completing this module you should be able to: describe, in detail, the structure and function of the dorsal column-medial lemniscal system (fasciculus gracilis and fasciculus cuneatus). given a lesion, identify the signs and symptoms that would be expected. given a patient case (examination results and chief complaint), identify the location of the lesion causing the signs and symptoms . correlate neurology information between the behavioral and neuroanatomical levels. Contents DCML Lesions Patient Cases Exit

Instructions This module contains 5 interactive lesion lessons with animation. Lesson lessons begin with a question about the symptoms produced by that particular lesion. Clicking the answer button will reveal the answer to the question. Clicking the explanation button will lead to both behavioral and neuroanatomical explanations of the lesion. Each presentation is launched by clicking the animation button. The same button serves to replay the animation if desired. Any of the 5 lessons may be accessed by simply clicking on the lesion title on the Contents page. Please refer to the legend that defines the symbols used throughout the module. Contents DCML Lesions Patient Cases Exit

Legend Mechanism of injury First-order neuron Lesion Second-order neuron Sensory stimulus Third-order neuron Light touch stimulus Sensory impairment Function intact Function lost Contents DCML Lesions Patient Cases Exit

Medial Lemniscal System Primary sensory cortex The Dorsal Column- Medial Lemniscal System Thalamus Nucleus Gracilis Nucleus Cuneatus Discriminative touch, vibration, and position information from the body is conveyed by the dorsal column-medial lemniscal system (DCML). The DCML is a crossed system. It originates from mechano-receptors (sensory receptors sensitive to mechanical deformation) located in the body wall and projects to the contralateral cerebral hemisphere via a three neuron projection system. The DCML is comprised of the fasciculus gracilis and fasciculus cuneatus. Fasciculus Cuneatus Fasciculus Gracilis Fasciculus gracilis Fasciculus cuneatus First-order neuron Second-order neuron Third-order neuron Stimulus Contents DCML Lesions Patient Cases Exit

Fasciculus Gracilis: Behavioral Description Primary sensory cortex Fasciculus Gracilis: Behavioral Description Thalamus Nucleus Gracilis Fasciculus gracilis Fasciculus gracilis: light touch, vibration, and position sense from the contralateral leg and lower trunk Consists of a 3-neuron projection system extending from receptors in the periphery to the primary somatosensory cortex (Click neuroanatomical explanation) Fasciculus Gracilis Click to animate Neuroanatomical Explanation First-order neuron Second-order neuron Third-order neuron Stimulus Fasciculus cuneatus Contents DCML Lesions Patient Cases Exit

Behavioral Explanation Fasciculus Gracilis: Neuroanatomical Description First-order neurons Cell body: dorsal root ganglion (DRG) Distal axon: innervates mechanoreceptors in leg and lower trunk via peripheral nerves Proximal axon: enter dorsal column (fasciculus gracilis), ascend ipsilaterally and terminate in the nucleus gracilis Second-order neurons Cell body: nucleus gracilis Axon: decussates in the medulla and projects to the contralateral thalamus (ventral posterior lateral nucleus, VPL) via the medial lemniscus Third-order neurons Cell body: VPL of thalamus Axon: ascends via the posterior limb of the internal capsule and terminates in the primary somatosensory cortex Click to animate Behavioral Explanation DRG Contents DCML Lesions Patient Cases Exit Fasciculus cuneatus

Fasciculus Cuneatus: Behavioral Description Primary sensory cortex Fasciculus Cuneatus: Behavioral Description Thalamus Nucleus Cuneatus Fasciculus Cuneatus Fasciculus cuneatus: Fasciculus cuneatus: light touch, vibration, and position sense from the contralateral arm and upper trunk Consists of a 3-neuron projection system extending from receptors in the periphery to the primary somatosensory cortex (Click neuroanatomical explanation) Click to animate Neuroanatomical Explanation First-order neuron Second-order neuron Third-order neuron Stimulus Contents DCML Lesions Patient Cases Exit

Behavioral Explanation Fasciculus Cuneatus: Neuroanatomical Description First-order neurons Cell body: dorsal root ganglion (DRG) Distal axon: innervates mechanoreceptors in arm and upper trunk via peripheral nerves Proximal axon: enter dorsal column (fasciculus cuneatus), ascend ipsilaterally and terminate in the nucleus cuneatus Second-order neurons Cell body: nucleus cuneatus Axon: decussates in the medulla and projects to the contralateral thalamus (ventral posterior lateral nucleus, VPL) via the medial lemniscus Third-order neurons Cell body: VPL of thalamus Axon: ascends via the posterior limb of the internal capsule and terminates in the primary somatosensory cortex Click to animate DRG Behavioral Explanation Contents DCML Lesions Patient Cases Exit

Lesion Lessons Fasciculus gracilis lesion Fasciculus cuneatus lesion Dorsal column lesion Medial lemniscus lesion Internal capsule lesion Contents DCML Lesions Patient Cases Exit

Lesion of the left fasciculus gracilis at T8 produces what impairment? Click for answer Damage to the left fasciculus gracilis at T8 causes the absence of light touch, vibration, and position sensation in the left leg and lower left trunk. Only the fasciculus gracilis exists below T6. Click for explanation Contents DCML Lesions Patient Cases Exit

Lesion of the fasciculus gracilis on the left: Behavioral Explanation Primary sensory cortex Lesion of the fasciculus gracilis on the left: Behavioral Explanation Thalamus Nucleus Gracilis Nucleus Cuneatus Fasciculus Cuneatus Fasciculus Gracilis Sensory impairment: absence of light touch, vibration, and position sensation in the left leg and lower left trunk. Sensory impairment: left leg and lower left trunk. Click to animate Neuroanatomical Explanation Lesion Lost function Impairment Contents DCML Lesions Patient Cases Exit

Lesion of the fasciculus gracilis on the left: Neuroanatomical Explanation Because the tract has not yet decussated, impairment is ipsilateral to the lesion. Lesion of first-order neurons interrupts ascending information so light touch, vibration, and position sensation is impaired in the left leg and lower left trunk. Receptors and reflex connections below the lesion level remain intact. Click to animate Behavioral Explanation Contents DCML Lesions Patient Cases Exit

Lesion of the left fasciculus cuneatus at C3 produces what impairment? Click for answer Damage to the left fasciculus cuneatus at C3 causes the absence of light touch, vibration, and position sensation in the left arm and upper left trunk. Click for explanation Contents DCML Lesions Patient Cases Exit

Lesion of the fasciculus cuneatus on the left: Behavioral Explanation Primary sensory cortex Thalamus Lesion of the fasciculus cuneatus on the left: Behavioral Explanation Nucleus Gracilis Nucleus Cuneatus Fasciculus Cuneatus Fasciculus Gracilis Sensory impairment: absence of light touch, vibration, and position sensation in the left arm and upper left trunk. Sensory impairment: left arm and upper left trunk. Click to animate Neuroanatomical Explanation Lesion Lost function Impairment Contents DCML Lesions Patient Cases Exit

Behavioral Explanation Lesion of the fasciculus cuneatus on the left: Neuroanatomical Explanation Because the tract has not yet decussated, impairment is ipsilateral to the lesion. Lesion of first-order neurons interrupts ascending information so light touch, vibration, and position sensation is impaired in the left arm and upper left trunk. Receptors and reflex connections below the lesion level remain intact. Behavioral Explanation Click to animate Contents DCML Lesions Patient Cases Exit

Lesion of the left dorsal columns at T2 produces what impairment? Click for answer Damage to the left dorsal columns at T2 causes the absence of light touch, vibration, and position sensation in the left side of the body below the lesion level (trunk, arm, and leg). Click for explanation Contents DCML Lesions Patient Cases Exit

Lesion of the dorsal columns on the left: Behavioral Explanation Primary sensory cortex Lesion of the dorsal columns on the left: Behavioral Explanation Thalamus Nucleus Gracilis Nucleus Cuneatus Fasciculus Cuneatus Sensory impairment: absence of light touch, vibration, and position sensation in the left side of the body below the lesion level (trunk, arm, and leg). Fasciculus Gracilis Sensory impairment: left side of the body, below the lesion level. Click to animate Neuroanatomical Explanation Lesion Lost function Impairment Contents DCML Lesions Patient Cases Exit

Lesion of the dorsal columns on the left: Neuroanatomical Explanation Because the lesion involves first-order neurons that have not yet decussated, impairment is ipsilateral to the lesion. Because both gracilis and cuneatus are damaged, light touch, vibration, and position sensation is impaired in the left trunk, leg and arm below the lesion level. Receptors and reflex connections below the lesion level remain intact. Behavioral Explanation Click to animate Contents DCML Lesions Patient Cases Exit

Lesion of the right medial lemniscus produces what impairment? Click for answer Damage to the right medial lemniscus causes the absence of light touch, vibration, and position sensation in the entire left side of the body from the neck down. Click for explanation Contents DCML Lesions Patient Cases Exit

Lesion of the medial lemniscus on the right: Behavioral Explanation Primary sensory cortex Thalamus Nucleus Gracilis Lesion of the medial lemniscus on the right: Behavioral Explanation Nucleus Cuneatus Fasciculus Cuneatus Sensory impairment: absence of light touch, vibration, and position sensation in the entire left side of the body from the neck down. Fasciculus Gracilis Sensory impairment: the entire left body, from the neck down. Click to animate Neuroanatomical Explanation Lesion Lost function Impairment Contents DCML Lesions Patient Cases Exit

Behavioral Explanation Lesion of the medial lemniscus on the right: Neuroanatomical Explanation Because the lesion involves second-order neurons that have already decussated, impairment is contralateral to the lesion. The medial lemniscus conveys light touch, vibration, and position sensation from the entire left trunk, leg and arm below the neck. Sensation from the face is unaffected because it is conveyed via cranial nerves. Behavioral Explanation Click to animate Contents DCML Lesions Patient Cases Exit

Lesion of the right internal capsule or primary somatosensory cortex produces what impairment? Click for answer Damage to the right internal capsule or primary somatosensory cortex causes the absence of light touch, vibration, and position sensation in the entire left side of the body including the face. Click for explanation Contents DCML Lesions Patient Cases Exit

Primary sensory cortex Thalamus Lesion of the internal capsule or primary somatosensory cortex on the right: Behavioral Explanation Nucleus Gracilis Nucleus Cuneatus Fasciculus Cuneatus Fasciculus Gracilis Sensory impairment: absence of light touch, vibration, and position sensation in the entire left side of the body including the face. Sensory impairment: the entire left body, including the face. Click to animate Neuroanatomical Explanation Lesion Lost function Impairment Contents DCML Lesions Patient Cases Exit

Behavioral Explanation Lesion of the internal capsule or primary somatosensory cortex on the right: Neuroanatomical Explanation Because the lesion involves third-order neurons that have decussated, impairment is contralateral to the lesion. The internal capsule conveys light touch, vibration, and position sensation from the entire left side of the body, trunk, leg, arm and face. Behavioral Explanation Click to animate Contents DCML Lesions Patient Cases Exit

Patient Cases Read these instructions! Patient Case 1 Patient Case 2 Contents DCML Lesions Patient Cases Exit

Case Instructions These patient cases are intended to facilitate the integration and clinical application of information about the DCML by coupling the findings on examination and patient interview with their neuroanatomical correlates. Each case begins with the patient’s chief complaint and significant examination findings. Then, the question is asked, Damage to what system(s) is causing this patient’s problems? Clicking the Answer button will reveal the answer and clicking the Show lesion button will reveal the neuroanatomic lesion along with the patient’s behavioral impairments. Cases are presented from two perspectives. What lesion would account for a given set of examination results and patient history? For a given lesion, what signs and symptoms would be expected on examination? Click on a Case number to begin the exercise. Contents DCML Lesions Patient Cases Exit

Case 1 Clumsiness and difficulty grasping with the left hand A left handed patient complains of “clumsiness” of her left arm and hand due to uncertainty of the limb’s position in space. She frequently fails to grasp or drops object with her left hand. Strength and AROM are WNL in all four extremities. Light touch, two-point discrimination, proprioception, and vibration sense are intact in the right upper extremity but absent in all dermatomes below the C3 dermatome in the left upper extremity. She is able to distinguish sharp from dull WNL in all four extremities and trunk, bilaterally. Damage to what system(s) is causing this patient’s problems? Answer Lesion of the left fasciculus cuneatus at approximately C3. Lateral corticospinal tracts are intact, bilaterally: strength and AROM are WNL in all four extremities. Lateral spinothalamic tracts are intact, bilaterally: sharp/ dull is WNL. Fasciculus gracilis is intact, bilaterally: light touch, two-point discrimination, proprioception, and vibration are WNL in bilateral lower extremities. Fasciculus cuneatus is absent on the left: light touch, two-point discrimination, proprioception (limb position in space), and vibration are absent in all dermatomes below C3 on the left but intact on the right upper extremity. Contents DCML Lesions Patient Cases Exit Show lesion

Lesion of the fasciculus cuneatus on the left: Behavioral Explanation Primary sensory cortex Thalamus Lesion of the fasciculus cuneatus on the left: Behavioral Explanation Nucleus Gracilis Nucleus Cuneatus Fasciculus Cuneatus Fasciculus Gracilis Sensory impairment: absence of light touch, vibration, and position sensation in the left arm and upper left trunk. Sensory impairment: left arm and upper left trunk. Click to animate Neuroanatomical Explanation Lesion Lost function Impairment Contents DCML Lesions Patient Cases Exit

Behavioral Explanation Lesion of the fasciculus cuneatus on the left: Neuroanatomical Explanation Because the tract has not yet decussated, impairment is ipsilateral to the lesion. Lesion of first-order neurons interrupts ascending information so light touch, vibration, and position sensation is impaired in the left arm and upper left trunk. Receptors and reflex connections below the lesion level remain intact. Behavioral Explanation Click to animate Contents DCML Lesions Patient Cases Exit

Case 2: Numbness and tingling on the left side of the body Following a brainstem stroke, the patient complains of numbness and tingling on the left side of the body. Sharp/dull and temperature sensation is unimpaired, throughout. 2 point discrimination on the fingertips are: 5 mm on the right and 15 mm on the left. In the absence of vision, the patient is able to identify common objects in the right hand but not the left and able to reproduce limb positions with the right lower extremity but not the left. Light touch and vibration sensation are WNL on the right but absent on the left side of the body. Pain and temperature as well as light touch, vibration and position sense are intact on both sides of the face. Strength and AROM are WNL in all four extremities. Damage to what system(s) is causing this patient’s problems? Lesion of the medial lemniscus on the right. Lateral corticospinal tracts are intact, bilaterally: strength and AROM are WNL in all four extremities. Lateral spinothalamic tracts are intact, bilaterally: sharp/ dull is WNL. Fasciculus gracilis is intact, bilaterally: light touch, two-point discrimination, proprioception, and vibration are WNL in bilateral lower extremities. Fasciculus cuneatus is absent on the left: light touch, two-point discrimination, proprioception (limb position in space), and vibration are absent in all dermatomes below C3 on the left but intact on the right upper extremity. Answer Contents DCML Lesions Patient Cases Exit Show lesion

Lesion of the medial lemniscus on the right: Behavioral Explanation Primary sensory cortex Thalamus Nucleus Gracilis Lesion of the medial lemniscus on the right: Behavioral Explanation Nucleus Cuneatus Fasciculus Cuneatus Sensory impairment: absence of light touch, vibration, and position sensation in the entire left side of the body from the neck down. Fasciculus Gracilis Sensory impairment: the entire left body, from the neck down. Click to animate Neuroanatomical Explanation Lesion Lost function Impairment Contents DCML Lesions Patient Cases Exit

Behavioral Explanation Lesion of the medial lemniscus on the right: Neuroanatomical Explanation Because the lesion involves second-order neurons that have already decussated, impairment is contralateral to the lesion. The medial lemniscus conveys light touch, vibration, and position sensation from the entire left trunk, leg and arm below the neck. Sensation from the face is unaffected because it is conveyed via cranial nerves. Behavioral Explanation Click to animate Contents DCML Lesions Patient Cases Exit

Case 3: Multiple Sclerosis A 34 year-old Caucasian female with a six year history of Multiple Sclerosis (exacerbating-remitting) has reported to the emergency room complaining of severe symptoms. A magnetic resonance image (MRI) of her spine shows a visible plaque, not seen in previous images, at the level of T10. The plaque involves the entire dorsal column on the left. What signs and symptoms would be expected from this lesion? Answer Lesion of the left dorsal column at T10 would impair (in the case of a large lesion possibly obliterate) light touch, vibration, and position sensation in the left leg and lower left trunk. Only the fasciculus gracilis exists below T6. Because she has the exacerbating-remitting type of MS, her previous symptoms will remain. If the DCML is the only system affected by this most recent exacerbation, the functions controlled by the corticospinal tract (voluntary movement) and lateral spinothalamic tract (pain and temperature sensation) would remain as before. Contents DCML Lesions Patient Cases Exit Show lesion

Lesion of the fasciculus gracilis on the left: Behavioral Explanation Primary sensory cortex Lesion of the fasciculus gracilis on the left: Behavioral Explanation Thalamus Nucleus Gracilis Nucleus Cuneatus Fasciculus Cuneatus Fasciculus Gracilis Sensory impairment: absence of light touch, vibration, and position sensation in the left leg and lower left trunk. Sensory impairment: left leg and lower left trunk. Click to animate Neuroanatomical Explanation Lesion Lost function Impairment Contents DCML Lesions Patient Cases Exit

Lesion of the fasciculus gracilis on the left: Neuroanatomical Explanation Because the tract has not yet decussated, impairment is ipsilateral to the lesion. Lesion of first-order neurons interrupts ascending information so light touch, vibration, and position sensation is impaired in the left leg and lower left trunk. Receptors and reflex connections below the lesion level remain intact. Click to animate Behavioral Explanation Contents DCML Lesions Patient Cases Exit

D. Michael McKeough, PT, EdD The End D. Michael McKeough, PT, EdD  2015